Democrats will "never" see President Donald Trump's tax returns, said White House chief of staff Mick Mulvaney, as a new front opened in the confrontation between the administration and Congress.

Mulvaney accused Democrats of engaging in a "political stunt" and wanting "attention" after the chairman of the House Ways and Means Committee, Rep. Richard Neal, asked the IRS to provide six years of Trump's personal tax returns and the returns for some of his businesses.